The present invention relates to a current tapping vane of a battery for end-side electrical resistance welding to a connecting strap in which that end region of the current tapping vane which is to be welded is bent transversely to the current tapping vane and is provided with weld burls at a bent end region, and to a process for making such a current tapping vane in which a sheet metal strip is inserted into a punching tool in a defined position and the current tapping vane is punched out from the sheet metal strip in accordance with its extended outline form and is provided, at the end region, with the weld burls for electrical resistance welding to a connecting strap, and the intended end region is bent over transversely to the flat side of the remaining current tapping vane.
A conventional current tapping vane can be either a thin current tapping vane, the thickness of which amounts to between 0.2 mm and 0.7 mm, and also thicker current tapping vanes with a thickness between 0.5 mm and 2.0 mm. Such a current tapping vane for a battery is formed, in general, of a sheet metal strip, at the one, electrode-side end region of which an electrode structure of fibrous construction is disposed. The production of these electrode plates preferably takes place by a resistance welding of the electrode structure to the current tapping vane. The electrode plates are stacked on one another with the intercalation of separators and, depending upon the polarity, electrically conductively connected to one another. The electrical connection of the electrode plates of the same polarity takes place in this case in that the current tapping vanes are welded, in particular by a resistance welding, at their other connecting strap-side end region to a connecting strap.
In order to simplify the welding, the connecting strap-side end regions of the current tapping vanes are bent transversely to the flat side of the other current tapping vane, preferably by an angle of approximately 90.degree.. Since the thickness of the material of the connecting strap and that of the current tapping vane differ greatly from one another (in general, the thickness of the material of the connecting strap is five times the thickness of the material of the current tapping vane) the connecting strapside, bent end region is provided with weld burls. In spite of these weld burls, it is repeatedly the case that incorrect or bad welding occurs.
An object of the present invention is to improve the known current tapping vane by improving the connection in the course of welding to the connecting strap and reducing the waste caused by welding defects in the course of welding of the current tapping vane to the connecting strap.
According to the present invention, the foregoing object has been achieved by providing that the weld burls are solid walls, and the current tapping vane is provided, at least in the bent end region, on both sides beside the weld burls, with one of interstices and reduced thickness portions, the depth of which is sized to be greater than a predetermined amount of settlement occurring during welding on, or the weld burls are material archings having sides which project transversely from the bent end region of the current tapping vane and merge with a radius of curvature corresponding to no greater than twice a wall thickness of the current tapping vane into the current tapping vane.
With respect to the novel process comprising the present invention, the foregoing object has been achieved by providing that after the bending over of the end region the weld burls are fitted into the latter by penetrating the current tapping vane or prior to the bending over of the end region the weld burls are fitted into the latter, in that a row of interstices are punched free from the lateral margin of the current tapping vane and spaced tongues are exposed.
According to the invention with respect to the two embodiments of the weld burls, melting takes place, during resistance welding, of the solid parts of the bent end region which are disposed between the material reductions or recesses, or the sides of the material archings which now do not spring back, to a large extent at the edge sides with the formation of good weld spots. In both embodiments, the quality of tile weld spots between the current tapping vane and the connecting strap is substantially improved.